Grab a variable names passed as function parameter

getVariableName.R

##' Return the name of variable \code{varname} in call \code{match_call}.                                                                             
##'                                                                                                                                                   
##' @title Return a variable name                                                                                                                     
##' @param match_call An object of class \code{call}, as returned by \code{match.call}.                                                               
##' @param varname An \code{character} of length 1 which is looked up in \code{match_call}.                                                           
##' @return A \code{character} with the name of the variable passed as parameter                                                                      
##' \code{varname} in parent close of \code{match_call}.                                                                                              
##' @examples                                                                                                                                         
##' a <- 1                                                                                                                                            
##' f <- function(x, y)                                                                                                                               
##'  getVariableName(match.call(), "x")                                                                                                     
##' f(x = a)                                                                                                                                          
##' f(y = a)                                                                                                                                          
##' @author Laurent Gatto
getVariableName <- function(match_call, varname) {
  match_call <- as.list(match_call)
  varname <- varname[1]
  mcx <- match_call[[varname]]
  while (any(sapply(mcx, length) != 1))
    mcx <- unlist(lapply(mcx, as.list))
  tail(as.character(mcx), n = 1)
}